Color-reactable inorganic adsorbent pigment and sensitized sheet material coated therewith



Dec. 28, 1965 G. A. HEMSTOCK 3,226,252

COLOR-REACTABLE INORGANIC ADSORBENT PIGMENT AND SENSITIZED SHEET MATERIAL COATED THEREWITH Filed Jan. 17, 1962 I KAOL/N CLAV ICALC/NAT/O/V AT 450%. TO 900 c.

DEHVDRATED CLAY SL/PP/NG AUTOCLAV/A/G I IPART/ALLV REHVDRATED CLAVI ICALC/NAT/ON AT 900 c. re //00 c.

[CRUSH/N6 AND MILL/NGI COLOR -REA CTABLE COA TING P/GMENT C OA TING OF SENS/77250 C OLOR-REAC TABL E, CALC/A/ED REHVDRATED AAOL l/V CLAY P/ GME N 7' COATING OF MICROSCOPIC RUPTURABLE CAPSULES CONTAIN- ING P/GMENT- SENSITIVE, NORMALLY COLORLE SS PRINT/N6 FLU/D INVENTOR GLEN A. HEMSTOCK ATTORNEY United States Patent 3,226,252 COLOR-REACTABLE INORGANIC ADSORBENT PEGMENT AND SENSITIZED SHEET MATE- RIAL (COATED THEREWITH Glen A. Hemstock, East Brunswick, NJ, assignor to Minerals & Chemicals Philipp Corporation, Menlo Park, N.J., a corporation of Maryland Filed Jan. 17, 1962, Ser. No. 166,912 5 Claims. (Cl. 117155) This invention generally relates to pressure-sensitive record material of the type utilizing multiple colorless, color-reactant materials which produce a colored mark upon adsorptive contact with each other, as exemplified by the manifold record material described in US. 2,730,456 to Barrett K. Green and Lowell Schleicher. More specifically, this invention has to do with an improvement in the sensitized color reactable coating member of the pressure-sensitive record material which serves as the print-receiving surface in conjunction with a printing fluid comprising normally colorless, color-reactable organic material that is converted to its colored form upon adsorptive contact with the sensitized coating. This invention is especially concerned with a novel adsorbent clay-like adsorbent pigment material which is employed in forming an improved sensitized coating for paper or other sheet material.

A type of manifold printing record material which obviates the use of carbon paper is produced by coating sheet material with a multiplicty of pressure rupturable microscopic capsules of a printing fluid comprising an oily vehicle and at least one normally colorless color-reactant organic material which turns to colored form upon contacting sheet material which has been properly sensitized. The manifold record material is assembled for manifold printing by stacking sheet material coated with encapsulated color-reactant organic material in face-to-face relationship with a sensitized coating on another sheet. Upon rupture of the capsules containing color-reactant material, as by printing pressure, the color-reactant organic material comes into adsorptive contact with the sensitized coating, producing a mark upon being transferred onto the sensitized coating. As in the production of other record forming material, the ultimate objective in formulating the constituents making up this type of record forming material is to obtain, at a reasonable cost, a very white printed sheet in which the print is registered accurately as uniform dark marks which clearly stand out from the white background.

One of the most practical forms of a manifold printing system of the type described above involves the use as the printing fluid of an encapsulated oily mixture of two particular color-reactant organic materials, namely, crystal violet lactone (3,3-bis(p-dimethylaminophenyl) 6-dimethylaminophthalide) and benzoyl leucomethylene blue. The crystal violet lactone produces a blue mark substantially immediately upon coming into adsorptive contact with a properly sensitized receiving sheet. This mark, however, is evanescent in nature and the benzoyl leucomethylene blue forms a substantially permanent blue mark before the initially formed mark fades. Therefore, a dark blue mark is present at all times after printing pressure is applied to the coating.

The print-receiving sheet is sensitized by having finely divided solid adsorbent particles uniformly present on a surface. The adsorbent solid is a clay-like material which is acid relative to the organic printing fluid. Color conversion of the color-reactant organic printing fluid materials results from an electron donor-acceptor solid surface chemical reaction between the printing fluid and the sensitized adsorbent particles.

The clay material that is commercially used in forming the sensitized print-receiving sheet when printing with the mixture of crystal violet lactone and benzoyl leucomethylene blue is calcined attapulgite clay. This particular type of clay is mixed with about 10% by weight of finely divided precipitated silica pigment. The silica is used to enhance the intensity of the initially formed mark since attapulgite clay used alone leaves something to be desired in this respect. This combination of pigment materials results in a coated receiving sheet which is exceptionally sensitive to a normally colorless mixture of crystal violet lactone and the leuco form of methylene blue. Therefore, sheet material coated with the mixed pigments acquires both a temporary and permanent dark blue color upon coming into adsorptive contact with the dye mixture.

However, the appearance of the attapulgite clay sensitized receiving sheet leaves much to be desired since the attapulgite clay coated sheet does not approach the whiteness of present day high grade coated paper stock. This is because attapulgite clay is of itself a yellowish material and it cannot be brightened appreciably without destroying its intrinsic character. The GE. brightness of the commercial sensitized receiving sheet made up with an attapulgite clay coating is only about 65 to 70% as compared with brightness values of to or more for paper stock coated with high grade kaolin clay, a very white clay material. While it might therefore appear to be a logical expedient to use kaolin clay in forming the sensitized coating for manifold record material when using crystal violet lactone and the leuco form of methylene blue as the printing fluid, this is not a satisfactory alternative. Kaolin clay, although it is an acid clay, is relatively insensitive to both crystal violet lactone and to the leuco form of methylene blue. As a result, only a very weak blue mark is obtained upon transfer of either of these materials to a sheet coated with kaolin clay. The mark is considerably too weak for practical usage and does not compare favorably with the intensity of the mark obtained with attapulgite clay.

Accordingly, it is an object of this invention to provide a sensitized receiving sheet of improved whiteness or brightness which will, however, register intense dark colored marks upon transfer of each of crystal violet lactone and benzoyl leucomethylene blue.

A more particular object of this invention is the provision of a treated kaolin clay product which is especially adapted for use as a coating pigment in producing an extremely white sensitized coating on a receiving sheet adapted for manifold printing with color-reactant organic compounds.

Another object of this invention is the provision from kaolin clay of a novel clay-like material whose cost compares favorably with the attapulgite clay mixture presently used in making up a sensitized coating for the receiving sheet of transfer printing material.

Still a further object of the invention is the provision of a sensitized pigment which produces a less viscous suspension in a starch vehicle than attapulgite clay at the same pigment level so that coating compositions made up with the pigment may be applied at higher pigment solids levels, thereby permitting higher machine speeds in the coating operation.

Further objects and advantages will be apparent from a description of this invention which follows, taken with the accompanying drawings in which:

FIGURE 1 is a flow sheet of the process for making the color-reactable coating pigment used in the practice of this invention; and

FIGURE 2 shows diagrammatically the manifold coated paper sheet of this invention.

This invention is a result of a surprising and unexpected discovery that the sensitivity of kaolin clay to colorless color-reactant printing fluids may be increased to exceptionally high levels by subjecting the clay, prior to use, to calcination and controlled hydrothermal treatment and thereafter to a very high temperature calcination, as described hereafter. This treatment results in an extremely white pigment which when coated on suitable sheet material forms a highly sensitized coating of exceptional whiteness.

Stated briefly, the novel adsorbent pigment of this invention is an amorphous, substantially anhydrous aluminum silicate of the approximate formula Al O -2SiO said silicate having been obtained by the following steps: (1) calcining kaolinite (a crystalline clay mineral of the approximate formula Al O -2SiO -2H O) at a temperature and for a time suflicient to remove substantially all the water of crystallization therefrom, thereby forming a material usually referred to as metakaolin, this material being an amorphous material of the formula Al O -2SiO (2) subjecting the metakaolin to hydrothermal treatment under superatmospheric pressure to restore most, but not all, of the theoretical water of crystallization to the metakaolin, this resulting in an amorphous, high surface area, hydrous aluminum silicate of the approximate formula Al O '2SiO (1.4-1.7)H O; and (3) calcining the resultant partially hydrated amorphous high surface area aluminum silicate at a temperature within the range of about 900 C. to 1100 C. for a time sufficient to remove substantially all of the water of composition therefrom.

Water of crystallization is calculated as follows:

(L.O.I.F.M.) X 100 (IOU-RM.)

L.O.I. in the equation represents loss on ignition which is determined by heating the clay to constant weight at 1000 C. RM. represents free moisture which is determined by heating the clay to constant weight at 105 C. For convenience sake, the water of composition of the partially rehydrated metakaolin intermediate product will be referred to hereafter as water of crystallization, although this product, like metakaolin, is amorphous. The term amorphous is used herein in its usual sense and refers to the state of a material which is apparently noncrystalline in that it does not diif-ract X-rays.

The sensitivity of calcined rehydrated metakaolin towards a mixture of crystal violet lactone and benzoyl leucomethylene blue differs substantially from the sensitivity to the mixture of any one of the following aluminum silicates of generally similar chemical composition: kaolin clay; calcined kaolin clay; the intermediate high surface area, partially rehydrated calcined kaolin from which the anhydrous aluminum silicate of this invention is obtained by calcination; or rehydrated metakaolin which has been calcined at temperature appreciably below 900 C. Thus, transfer of a mixture of crystal violet lactone and benzoyl leucomethylene blue into contact with a sheet coated with the high temperature calcined rehydrated metakaolin of this invention results in an immediate and permanent intense blue coloration at the site of adsorptive contact. On the other hand, upon adsorptive contact of a mixture of these organic printing fluids with the parent kaolin or calcined kaolin, only a weak immediate mark as well as a weak permanent blue mark results. The rehydrated metakaolin from which the product of this invention is obtained by high temperature calcination immediately produces a dark coloration upon adsorptive contact with the color-reactant mixture; however, the mark is transient, indicating that the partially rehydrated material is color reactable only with the crystal violet lactone and that the crystal violet lactone is relatively insensitive towards an acid clay material of this nature. The same is true of the material obtained by rnildly calcining the rehydrated metakaolin. Surprisingly, the novel silicate pigment of this invention is no more acid than kaolin clay or than the intermediate silicates obtained in its production. Therefore, the superiority in sensitivity of the high temperature Percent Water of Crystallization= calcined rehydrated metakaolin over the other kaolintype materials cannot be accounted for on this basis.

Paper coated with the anhydrous aluminum silicate pigment of this invention is considerably whiter than paper coated with attapulgite clay or a mixture of attapulgite clay and silica pigment. Thus, whereas a representative sample of a commercial print-receiving sheet which has been coated with a mixture of attapulgite clay and silica has a G.E. brightness value of only 65 to paper coated with the novel silicate of this invention as the sole coating pigment has a brightness of or more, depending principally on the brightness value and thus the purity of the starting kaolin clay from which the pigment is obtained. Therefore, when the coated sheet of this invention is subjected to printing using a mixture of benzoyl leucomethylene blue and crystal violet lactone, the printed record is a very white sheet containing clear dark blue markings which stand out from the background. This result is obtained at a cost which is no greater than that of the attapulgite clay-colloidal silica mixture heretofore used. Moreover, the whiteness of the pigment of this invention exceeds substantially that of the parent kaolin, metakaolin, partially rehydrated metakolin or even rehydrated metakaolin calcined at temperatures appreciably below 900 C.

Yet another important advantage of using the novel anhydrous amorphous aluminum silicate in the production of the sensitized coating rather than an attapulgite clay-colloidal silica formulation is that the nature of the amorphous silicate pigment is such that a coating color made up therewith can be applied to paper at a considerably higher pigment solids loading. This means in practice that higher machine speeds may be used in coating paper with the pigment. Using the pigment of this invention, coating colors containing 40 to 45% pigment solids may be employed. In contrast, 35% solids is about the highest pigment loading feasible with attapulgite clay.

The method for producing the novel sensitized aluminum silicate pigment of this invention and the application of the use of this pigment to manifold printing will be more fully understood by the following detailed de scription thereof.

PREPARATION OF METAKAOLIN Kaolin clay (a clay consisting for the most part of the mineral kaolinite) is refined to the extend that grit (particles coarser than 44 microns) and undispersible agglomerates are removed. Coarse or fine fractions of clay may also be used, if desired. Clays which have received other preliminary treatment, such as deironing or other benefication, may be employed provided such treatment does not entail appreciable removal of alumina or silica from the clay. The clay is pulverized to render it all finer than about 325 mesh.

The crushed clay is initially calcined to eliminate substantially completely the water of crystallization, thereby converting the kaolin to metakaolin. The water of crystallization of the calcined product should not be more than about 2% and is preferably less than 1% to obtain the maximum benefit of the subsequent hydrothermal treatment. In practice, difficulty may be experienced in eliminating completely water of crystallization, and a water of crystallization of about 0.2% to 0.5% by weight in the metakaolin may be as low as can be practically attained.

Calcination is carried out in air or steam, at atmospheric pressure or under vacuum, if desired. The temperature at which calcination is conducted, provided it is sufficient to effect substantial dehydration, is below that temperature at which the characteristic kaolin exotherm occurs (940980 C.). Calcination temperature is critical only to the extent that the temperature must be high enough to effect substantially complete conversion of the hydrous clay to metakaolin and yet be below that at which the kaolin exotherm occurs. Calcination periods will usually fall within the limits of about /2 hour to 20 hours or more at temperatures of from about 450 C. to about 900 C. Calcin-ing at temperatures below about 450 C. does not result in adequate loss of water of crystallization from the clay, even if calcination time is prolonged. When the clay is calcined above about 900 C. for a time sufficient to permit the kaolin exotherm to take place a profound change in the morphology of the calcined product occurs and pure metakaolin is not produced. Instead, a very dense material, believed by some authorities to be incipient mullite, is produced and this material is not amenable to the hydrothermal treatment hereafter set forth. The kaolin structure is substantially destroyed by the calcination as is evidenced by the absence of characteristic kaolin lines in the X-ray diffraction pattern of the calcined product.

HYDROTHERMAL TREATMENT OF METAKAOLIN The metakaolin is cooled prior to hydrothermal treatment, since it has been found that when hot metakaolin is subjected to hydrothermal treatment such as to restore the controlled amount of water of crystallization, the resulting product does not have the desired high surface area of the material produced when the metakaolin is cooled before undergoing hydrothermal treatment. Cooling is conducted in air or in an inert atmosphere until the metakaolin reaches ambient temperature or somewhat higher, but below about 125 C.

An aqueous slip of metakaolin is then prepared. The solids content of the slip may vary widely and good results have been realized operating with slips as dilute as solids (based on the composition weight) or as concentrated as 50% solids. More dilute slips may be used although for practical reasons slips less concentrated than 10% are not recommended. Apparatus and procedures for preparing clay slips are well known to those skilled in the art.

The clay, in the form of an aqueous slip or paste, is subjected to hydrothermal treatment with saturated high pressure steam under conditions of time selected to restore water of crystallization to the dehydrated aluminum silicate in the amount within the limits of about 10% to about 12%, which is less than the theoretical water of crystallization of naturally occurring kaolin clay (13.9%). If desired, the slip may be formed in situ in the bomb when the calcined material is contacted with steam. Any suitable pressurized equipment provided with means for introducing and controlling pressurized steam may be employed. The hydrothermal treatment is carried out by directly contacting the metakaolin slip with saturated steam at a temperature up to, but not including, the critical temperature of water. As shown in applicants copending application, Serial No. 852,168, referred to hereinafter, a convenient method for carrying out the hydrothermal treatment of the metakaolin slip is to heat the slip in an autoclave or the like until the desired steam pressure is attained and maintain the slip under such pressure for a suitable time. The desired results are not obtained using superheated steam. Since rehydration will be appreciably more rapid operating with saturated steam at relatively high pressure, the preferred hydrothermal treatment is conducted with saturated steam at or above 800 p.s.i.g. For example, the desired degree of rehydration will be accomplished operating under the following approximate operating conditions using steam at saturation temperature: 300 p.s.i.g., for 60 hours; 400 p.s.i.g., for 28 hours; 500 p.s.i.g., for 8 hours; 800 p.s.i.g., for 2 /2 hours; 1000 p.s.i.g., for 1 hour; 1400 p.s.i.g., for 30 minutes; and 1600 p.s.i.g., for 0 minutes. Time conditions refer to time after the reaction vessel reaches the indicated saturated steam pressure.

Rehydration may also be carried out on pressed cakes of metakaolin and such pressed cakes may be prepared by calcining mechanically compressed kaolin clay or by mechanically compressing finely divided metakaolin, preferably the former. However, it will be noted that clay which has been pressed (e.g., pelleted) before or after calcination does not necessarily respond to hydrothermal treatment as does pulverized clay and the desired high surface area product is obtained from pressed clay with high pressure saturated steam only when the density of the pressed product is between about 1.1 and 1.5 grams per cubic centimeter and hydrothermal conditions preselected to restore about 8.5% to about 12% water of crystallization to the dehydrated material.

The product obtained by hydrothermally treating metakaolin, under conditions described above, results in a high surface area hydrous aluminum silicate having a surface area within the range of about 120 to 300 square meters per gram, sometimes more. These surface area values are considerably higher than those of raw kaolin clay or metakaolin which normally have surface areas of only 5 to 15 square meters per gram. Surface area values referred to in the specification and claims are so-called B.E.T. values, determined by a nitrogen adsorption method described by S. Brunauer, P. H. Emmett and E. Teller in their article entitled Adsorption of Gases in Multi-Molecular Layers, on page 309 of Journal of the American Chemical Society, vol. 60, February 1938, using the molecular size data of H. K. Livingston presented in his article entitled Cross-Sectional Areas of Molecules Adsorbed on Solid Surfaces, on page 569 of Journal of the American Chemical Society, vol. 66, April 1944.

The surface area of the hydrous aluminum silicate obtained by hydrothermal treatment of metakaolin has been found to be independent of the temperature at which kaolinite is dehydrated to form metakaolin. The surface area is also independent of steam pressure and reaction time employed in the hydrothermal treatment since substantially the same product can be obtained by hydrothermal treatment at different saturated steam pressures. However, the surface area is apparently related to the amount of chemically combined water introduced into the metakaolin during hydrothermal treatment and to the amount of crystal structure obtained as measured by the intensity of the 7.2 A. d spacing on the X-ray diffraction pattern. Kaolin clay has an intense 7.2 A. d spacing on its X-ray diffraction pattern, indicating a well-crystallized structure. Some samples of the high surface area, partially rehydrated metakaolin have a very weak 7.2 A. 20 line indicating the presence of kaolinite only as a minor impurity. Other samples, especially those having an exceptionally high surface area, exhibit No. 7.2 A. d spacing.

Reference is made to the inventors copending patent application, Serial No. 852,168, filed November 12, 1959, now abandoned, for illustrative examples of the rehydration of kaolin clay to produce an amorphous high surface area partially rehydrated metakaolin.

CALCINATION OF REHYDRATED METAKAOLIN TO OBTAIN COLOR SENSITIZED PIGMENT Calcination of the high surface area rehydrated metakaolin at 900 C. to 1100 C. for a time sufficient to eliminate substantially water of composition therefrom results in the amorphous anhydrous aluminum silicate color sensitized pigment product of this invention. Especially recommended is a calcination temperature of about 1000 C. It will be noted that the temperature at which the rehydrated metakaolin is calcined to produce the pigment of this invention is higher than that at which kaolin clay is calcined to convert it into metakaolin. The surface area (B.E.T.) of the calcined product is normally within the range of from about 50 to about square meters per gram, depending principally on the surface area of the rehydrated metakaolin precursor and the calcination temperature. When calcination is carried out at temperatures below about 900 C., the resultant calcined pigment is not sensitized towards the crystal violet lactone dye as when calcination is carried out at a temperature within the range of 900 C. to 1100 C. Moreover, the pigment obtained by calcination at 900 C. to 1100 C. is considerably whiter than that obtained by calcination of rehydrated metakaolin at lower temperature. On the other hand, calcination temperatures above 1100 C. may result in the development of undesirable crystalline phases in the pigment product. Calcination time, which will vary with the calcination equipment and efliciency of contact of the material being calcined With the atmosphere in the calciner, will usually fall within the limits of M2 hour to 20 hours or more. The water of crystallization of the calcined rehydrated metakaolin does not exceed 1%.

The calcined material is crushed and milled to a suitable size for use as a coating pigment, e.g., to an average particle size of 10 microns or finer.

FORMATION OF SENSITIZED COATED SHEET MATERIAL Color-reactant sensitized sheet material is made up by applying an aqueous dispersion of the finely divided calcined rehydrated metakaolin to at least one surface of a suitable sheet material, usually paper. A water-dispersible adhesive such as starch, butadiene-styrene, latex, casein or mixtures thereof, is incorporated with the aqueous dispersion as a binder for the pigment. Normally a pigment dispersant, such as, for example, a molecularly dehydrated phosphate, is also incorporated in the dispersion. The pigment coating is uniformly applied to a base sheet by any of the familiar types of coating equipment. The coating is applied to the base sheet in amount such as to provide a uniform coat about 0.0005 inch thick. The base sheet is usually paper stock although other sheet material, such as, for example, glass, plastics or paper board, may be employed inasmuch as the base material performs no active part in the printing process and serves merely as a carrier for the sensitized pigment.

While in the preferred form of this invention, calcined rehydrated metakaolin is the sole pigment used in forming the sensitized coating, other sensitized pigments, such as attapulgite clay, may be employed in conjunction with the calcined rehydrated metakaolin; the calcined rehydrated metakaolin, however, should be present in amount in excess of 50% by Weight of the total adsorbent pigment solids in order that the character of the calcined rehydrated metakaolin will predominate in determining the character of the coating.

The adsorbent pigment coating constitutes the front surface of an improved manifold record material of this invention; the rear surface which forms the transfer coating of the sheet material is coated with a multiplicity of microscopic rupturable capsules containing oil, crystal violet lactone and benzoyl leucomethylene blue. In manifold printing, a plurality of these sheets are stacked in a manner such that the adsorbent pigment coated surface of one sheet is in face-to-face relationship with a coating of ruptur-able encapsulated printing fluid of another sheet. In practice, in forming manifold record material, the pigment coating is normally applied to the Wire side of a sheet of raw stock and an emulsion coating containing printing fluid is applied to the felt side. Suitable transfer coating compositions and methods for producing a coating of a multiplicity of microscopic oil-containing encapsulated printing fluid are described in detail in US. 2,730,456 to Barrett K. Green and Lowell Schleicher. However, means for forming a coating of microscopic rupturable capsules other than the means described in said patent may be used in producing the transfer coating adapted for use with the coating of sensitized clay-like pigment of this invention since the sensitivity of the pigment is generally independent of the particular composition of the rupturable capsule shell containing the crystal violet lactone-benzoyl leucomethylene blue mixture.

A typical composition of encapsulated printing fluid comprises about equal weight proportions of crystal violet lactone and benzoyl leucomethylene blue dissolved in trichlorodiphenyl or other water-immiscible oil.

Also in accordance with this invention, the sensitized clay coating may be applied as a layer over a previously formed coating of encapsulated organic color-reactant materials or the latter coating may be applied directly over a layer of the pigment coating.

The following example illustrates the preparation of the sensitized adsorbent aluminum silicate pigment of this invention and its unique properties. It is of course understood that the material and its method of preparation are exemplary and are not to be considered to limit the inven tion to the particularly operating conditions described.

The starting clay used in the production of a sensitized pigment of this invention was a water-washed, degritted fine fraction of kaolin clay from a mine near McIntyre, Georgia. The clay was composed primarily of Wellcrystallized kaolinite and had an average equivalent spherical diameter of about 0.8 micron. The kaolin clay was pulverized in a high speed hammer mill and calcined in a preheated muffle furnace at 700 C. for 4 hours to produce metakaolin. The metakaolin was cooled to room temperature, pulverized and made into a 10% solids slip. The aqueous slip was placed in a stainless steel autoclave and subjected to the action of saturated steam at 1000 p.s.i.g. for one hour.

The rehydrated metakaolin was pulverized in a high speed hammer mill and calcined in a preheated mufiie furnace at 1000 C. for one hour. For purposes of comparison a portion of the rehydrated metakaolin was calcined in the muffle furnace at 700 C. for one hour, this temperature being well below that required to develop optimum properties in the rehydrated metakaolin.

The surface area and water of crystallization of the starting clay, intermediate products and calcined rehydrated metakaolin products are given below.

Table I.-Pr0perties of heat and/or hydrothermally treated aluminum silicates Base sheets for color reaction with organic color-reactable printing fluid were produced with each of the aboveidentified pigment samples as the coating pigment. The

solids of the coating compositions were as follows:

Parts by wt.

Aluminum silicate pigment Quadrafos (a complex phosphate having a P O :Na O ratio corresponding to the formula NEIGP4O13) Sodium silicate (38% solids suspension, SiO :Na O

ratio of 3.2:1) 3.6 Enzyme converted starch 6.0 Styrene-butadiene latex 9.7 Casein 0.9 Santomerse (aralkyl sulfonate wetting agent) 0.3

The general procedure for preparing coating colors was as follows: cooked casein was soaked in water at approximately 20% solids for 10 minutes prior to the addition of a pint of 28% ammonium hydroxide. The temperature of the casein suspension was raised to F. and maintained at that temperature for 10 minutes. A latex mixture was prepared by dispersing 2 pounds of wetting agent (Santomerse) in water and adding pounds of 48% solids latex. Six pounds (dry weight) of the cooked casein was then added to the latex system. Enzyme converted starch was made by mixing starch at about 25% solids and 1 gram of enzyme was added to each pound of starch. The mixture was cooked for a total of 55 min- 9 utes, gradually raising the cooking temperature from 160 F. to 210 F.

Quadrafos and sodium silicate (pigment dispersants) were added to water prior to addition of aluminum silicate pigment. The latex-casein mixture was added to the pigment suspension and the enzyme converted starch was incorporated.

Sheets of raw paper stock were coated with experimental coating colors made up with each of the aluminum silicate pigment samples identified in Table 1. Sheets were also made up with a coating color in which the pigment was a mixture of 90 parts by weight of Attasorb RVM, a calcined fluid energy milled attapulgite clay and 10 parts by weight of finely divided silica gel.

In coating with the aluminum silicate pigment samples, an initial coating was applied at 40% solids at the rate of /4-1 pound per ream (25" x 40500). The sheet was dried to a moisture content in the range of to and the sheet was passed through two successive roll coaters, each of which applied 1 /2 to 1% pounds per ream of coating at 45% solids. In coating with the attapulgite coating color, coating was at only about to solids since higher pigment sol-ids could not be used.

The sensitivity of crystal violet lactone and benzoyl leucomethylene blue towards each of the coated sheets was determined by placing a commercial emulsion colorreaotant coated paper containing encapsulated oil, crystal violet lactone and benzoyl leucomethylene blue directly over and into contact with the pigment coated sheet. The two sheets were simultaneously passed through a calender under pressure sufficient to rupture the microscopic capsules and liberate the printing fluid mixture. The results are summarized in Table II. Also reported in this table are G.E. block brightness values of the pigment of this inyention and of the calcined attapulgite clay-colloidal silica mixture of the prior art.

sufficient to remove substantially all of the water of hydration therefrom.

2. A sensitized color-reactable coating pigment consisting of a white amorphous aluminum silicate of the approximate formula Al O -2SiO said silicate having a B.E.T. surface area within the range of about to about 100 sq. m./ gm. and having been obtained by hydrothermally rehydrating metakaolin at superatmospheric pressure to obtain an amorphous aluminum silicate of the approximate formula Al O -2SiO (1.4-1.7 H 0) and having a B.E.T. surface area of at least about 120 sq. m./gm., and calcining said rehydrated metakaolin at a temperature within the range of 900 C. to 1100 C. fora time sufficient to remove substantially all of the water of hydration therefrom, said pigment particles being further characterized by producing an intense blue color upon being put into adsorptive contact with normally colorless crystal violet lactone and with normally colorless benzoyl leucomethylene blue, whereby said pigment is capable of being used as a coating for record sheet material in printing with a mixture of said normally colorless organic materials.

3. Sheet material having a sensitized color-reactable adsorbent surface coating comprising the pigment of claim 2 in amount sufiicient to provide a white pigmented coating on said sheet material.

4. Paper having coated on a surface thereof a sensitized colonreactable adsorbent surface coating comprising the pigment of claim 1 in amount sufiicient to provide a white pigmented coating on said paper.

5. Paper having a sensitized color-reactable surface coating comprising pigment particles, the major portion of which are white particles of an amorphous aluminum silicate of the approximate formula Al O -2SiO said silicate having a B.E.T. surface area within the range of about 50 to about 100 sq. m./gm. and having been obtained Table II.Efiect of nature of coating pigment on transfer printing with encapsulated crystal violet lactone and benzoyl leucomelhylene blue printing fluid Appearance of Printed Sheet Kaolin Clay (1) Calcined at 700 074 hrs (2) Rehydrated at 1,000 p. (3) calcined at 700 C./1 h (3) Calcined at 1,000 G./1 hr 1. 2. 3. 4. 5. 6. Attapulgite Clay-Silica Gel Mixture These data show that only pigment sample 5 (the rehydrated metaka-olin calcined at 1000 C.) matched the immediate and permanent sensitivity of the commercial attapulgite clay pigment mixture (pigment sample 6). The pigment brightness values in the table show that the pigment of this invention is considerably whiter than the prior art pigment mixture, indicating that sheet material sensitized with calcined rehydrated metakaolin will be considerably brighter than sensitized sheets heretofore used for the purpose.

I claim:

1. A sensitized color-reactable coating pigment consisting of a white amorphous aluminum silicate of the approximate formula Al O -2SiO said silicate having a B.E.T. surface area within the range of about 50 to about 100 sq. m./lgm. and having been obtained by hydrothermally rehydrating me-takaolin at superatmospheric pressure to obtain an amorphous aluminum silicate of the approximate formula Al O -2SiO -(1.41.7 H 0) and having a B.E.T. surface area of at least about 120 sq. m./gm., and calcining said rehydrated metakaolin at a temperature within the range of 900 C. to 1100 C. for a time References Cited by the Examiner UNITED STATES PATENTS 2,477,664 '8/1949 Shabaker 252-449 XR 2,618,573 11/1952 Green 117-36.8 2,730,457 1/1956 Green 1l7--36.'8 3,014,836 12/1961 Pr-octer 117-152 XR OTHER REFERENCES Laird: J. Am. Ceramic 500., v. 2, 1919, pp. 828-832.

WILLIAM D. MARTIN, Primary Examiner.

' MURRAY KATZ, RICHARD D. NEVIUS, Examiners. 

5. PAPER HAVING A SENSITIZED COLOR-REACTABLE SURFACE COATING COMPRISING PIGMENT PARTICLES, THE MAJOR JPORTION OF WHICH ARE WHITE PARTICLES OF AN AMORPHOUS ALUMINUM SILICATE OF THE APPROXIMATE FORMULA AL2O3$2SIO2, SAID SILICATE HAVING A B.E.T. SURFACE AREA WITHIN THE RANGE OF ABOUT 50 TO ABOUT 100 SQ. M./GM. AND HAVING BEEN OBTAINED BY HYDROTHERMALLY REHYDRATING METAKAOLIN AT SUPERATMOSPHERIC PRESSURE TO OBTAIN AN AMORPHOUS ALUMINUM SILICATE OF THE APPROXIMATE FORMULA AL2O3$2SIO2(1.4-1.7) H2O AND HAVING A B.E.T. SURFACE AREA OF AT LEAST ABOUT 120 SQ. M./GM., AND CALCINING SAID REHYDRATED METAKAOLIN AT A TEMPERATURE WITHIN THE RANGE OF 900*C. TO 1100*C. FOR A TIME SUFFICIENT TO REMOVE SUBSTANTIALLY ALL OF THE WATER OF HYDRATION THEREFROM. 